HttpContext.Current.User.Identity.Name is always string.Empty

Hi I use a custom MembershipProvider.
I want to know the current username during an application scenario, but when I try accessing HttpContext.Current.User.Identity.Name it always returns string.Empty.
Example:
bool x = User.Identity.IsAuthenticated; //true string y = User.Identity.Name; //""
 
Am I missing something?
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